The virus family Caliciviridae consists of four genera is a family of positive-strand RNA viruses: (1) "Norwalk like viruses" (with species Norwalk virus) (2) "Sapporo-like viruses" (with species Sapporo virus); (3) Vesivirus (with species, feline calicivirus and vesicular exanthema of swine virus); and (4) Lagovirus (with species rabbit hemorrhagic disease virus and European brown hare syndrome virus). Norwalk virus (NV) is the prototype strain for the Norwalk-like viruses (NLVs), and was discovered by LID researchers in 1972. The NLVs are the major cause of nonbacterial epidemic gastroenteritis that occurs in family, school, institutional, or community-wide outbreaks, affecting all age groups. The NLVs are genetically diverse and cannot be grown in cell culture, which has been a continuing research obstacle. This year, we continued our work in the development of systems and animal models to study the biology and replication of the NLVs. The systems include: (1) expression of NLV proteins from cloned genes in several different expression vectors for the development of diagnostic assays for use in epidemiologic studies and for the analysis of protein function; and (2) studies using our feline calicivirus (FCV) reverse genetics system that includes an infectious cDNA clone and a permissive cell culture system. There were two calicivirus animal models that were explored further this year: (1) infection of chimpanzees with NLVs from human stool material in preparation for RNA transfection studies using transcripts derived from a full-length cDNA clone; and (2) infection of mink with mink enteric calicivirus (a "Sapporo-like calicivirus") in an effort to develop a small animal model for calicivirus diarrhea. The long-term goal of this project is to elucidate the role of the NLVs in diarrheal disease and to develop strategies to lessen the disease burden.